class Solution {
    public int minimumDeleteSum(String s1, String s2) {
        int len1 = s1.length();
        int len2 = s2.length();
        int[][] dp = new int[len1 + 1][len2 + 1];
        dp[0][0] = 0;
        for(int i = 1; i <= len1; i ++) {
            dp[i][0] = dp[i - 1][0] + s1.charAt(i - 1);
        }
        for(int j = 1; j <= len2; j ++) {
            dp[0][j] = dp[0][j - 1] + s2.charAt(j - 1);
        }
        for(int i = 1; i <= len1; i ++) {
            for(int j = 1; j <= len2; j ++) {
                if(s1.charAt(i - 1) == s2.charAt(j - 1)) {
                    dp[i][j] = dp[i - 1][j - 1];
                } else {
                    dp[i][j] = min(dp[i - 1][j] + s1.charAt(i - 1),
                                  dp[i][j - 1] + s2.charAt(j - 1));
                }
            }
        }
        return dp[len1][len2];
    }

    private int min(int a, int b) {
        return a < b ? a : b;
    }
}
